The present invention relates generally to an electromagnetically operating actuator for control elements capable of making oscillatory movements in displacement machines, more particularly for flat slide shut-off valves and lift valves, comprising a spring system and two electrically operating switching magnets, over which the control element is movable in two discrete opposite operating positions and is retained thereat by either switching magnet, the locus of the position of equilibrium of the spring system lying between the two operating positions.
Displacement machines require an adaptive control to allow the working fluid to flow in and out for optimum control of the working process in order to achieve the objectives required in each case. The sequential control exerts a great influence on the various parameters, e.g., the conditions of the working fluid before, in, and after the working space, the operating frequency, and the processes in the working space. The need for adaptive control particularly exists in internal combustion engines, because under very different operating conditions they operate unsteadily and a suitably varied positive control of the gas-exchange valves is of advantage.
Heretofore, camshafts have essentially been employed to control the gas-exchange valves in internal combustion engines. However, they do not permit variable control. In addition, electromagnetic controls of gas-exchange valves are known in the art for internal combustion engines in which a spring applies the closing force to the gas-exchange valve, while the opening forces are generated by a properly controlled solenoid. This type of electromagnetic control has the disadvantage that short control periods in the case of high operating frequencies and conventional lifts of the gas-exchange valves can only be produced with extensive switchgear and with a great expenditure of energy (see, for example, DOS 28 15 849, and DOS 20 63 158). Furthermore, as exemplified by DOS 23 35 150, an electromagnetically operating control system for gas-exchange valves is disclosed for internal combustion engines, and comprises two water-cooled tapped winding coils each interacting with an armature. Both armatures are affixed to a common spindle which acts on the gas-exchange valve. As in the case of a cam control, this gas-exchange valve has a compression spring which holds the valve in a closed position. Another spring is provided with identical spring stiffness, which acts on either armature and is subjected to a compressive stress by the armature while the valve is closed. To operate such device, one solenoid is energized, while the other is de-energized. Owing to the initially stressed spring system, the valve spindle is accelerated with the armature until its half-stroke position is reached, where both armatures are spaced the same distance from their operating coils. These switching coils are designed in such a way that, after energization, they can attract their armatures from this central position against the intensifying force of the spring system. In the rest position of this arrangement, both armatures also place themselves in their middle position, so that the gas-exchange valve has already reached its half-stroke position, causing it to open.
This arrangement has the drawback that for all practical purposes it cannot be employed in internal combustion engines, because stopping the internal combustion engine, in some cases over fairly long periods of time with the gas-exchange valves open in all cylinders, can lead to corrosion in the cylinders. Another disadvantage is that in order to start an internal combustion engine so equipped, the switching coils must be designed for attracting an armature beyond the half-stroke position for great forces over large distances, which means very substantial energy requirements for starting a multicylinder internal combustion engine. Furthermore, a disadvantage in such an arrangement is that, because of the large masses of the two plunge armatures to be accelerated, a high switching frequency can only be produced by means of considerable spring tensions, so that the necessary magnetic forces and, thereby, the energy requirements are greatly increased.